Re: [PATCH RFC 33/43] objtool: Add validation for x86 PIE support

[Christophe Leroy]

Le 28/04/2023 à 11:51, Hou Wenlong a écrit :
> [Vous ne recevez pas souvent de courriers de houwenlong.hwl@xxxxxxxxxxxx. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
> 
> For x86 PIE binary, only RIP-relative addressing is allowed, however,
> there are still a little absolute references of R_X86_64_64 relocation
> type for data section and a little absolute references of R_X86_64_32S
> relocation type in pvh_start_xen() function.
> 
> Suggested-by: Lai Jiangshan <jiangshan.ljs@xxxxxxxxxxxx>
> Signed-off-by: Hou Wenlong <houwenlong.hwl@xxxxxxxxxxxx>
> Cc: Thomas Garnier <thgarnie@xxxxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
>   arch/x86/Kconfig                        |  1 +
>   scripts/Makefile.lib                    |  1 +
>   tools/objtool/builtin-check.c           |  4 +-
>   tools/objtool/check.c                   | 82 +++++++++++++++++++++++++
>   tools/objtool/include/objtool/builtin.h |  1 +
>   5 files changed, 88 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 715f0734d065..b753a54e5ea7 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2224,6 +2224,7 @@ config RELOCATABLE
>   config X86_PIE
>          def_bool n
>          depends on X86_64
> +       select OBJTOOL if HAVE_OBJTOOL
> 
>   config RANDOMIZE_BASE
>          bool "Randomize the address of the kernel image (KASLR)"
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index 100a386fcd71..e3c804fbc421 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -270,6 +270,7 @@ objtool-args-$(CONFIG_HAVE_STATIC_CALL_INLINE)              += --static-call
>   objtool-args-$(CONFIG_HAVE_UACCESS_VALIDATION)         += --uaccess
>   objtool-args-$(CONFIG_GCOV_KERNEL)                     += --no-unreachable
>   objtool-args-$(CONFIG_PREFIX_SYMBOLS)                  += --prefix=$(CONFIG_FUNCTION_PADDING_BYTES)
> +objtool-args-$(CONFIG_X86_PIE)                         += --pie
> 
>   objtool-args = $(objtool-args-y)                                       \
>          $(if $(delay-objtool), --link)                                  \
> diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
> index 7c175198d09f..1cf1d00464e0 100644
> --- a/tools/objtool/builtin-check.c
> +++ b/tools/objtool/builtin-check.c
> @@ -81,6 +81,7 @@ static const struct option check_options[] = {
>          OPT_BOOLEAN('t', "static-call", &opts.static_call, "annotate static calls"),
>          OPT_BOOLEAN('u', "uaccess", &opts.uaccess, "validate uaccess rules for SMAP"),
>          OPT_BOOLEAN(0  , "cfi", &opts.cfi, "annotate kernel control flow integrity (kCFI) function preambles"),
> +       OPT_BOOLEAN(0, "pie", &opts.pie, "validate addressing rules for PIE"),
>          OPT_CALLBACK_OPTARG(0, "dump", NULL, NULL, "orc", "dump metadata", parse_dump),
> 
>          OPT_GROUP("Options:"),
> @@ -137,7 +138,8 @@ static bool opts_valid(void)
>              opts.sls                    ||
>              opts.stackval               ||
>              opts.static_call            ||
> -           opts.uaccess) {
> +           opts.uaccess                ||
> +           opts.pie) {
>                  if (opts.dump_orc) {
>                          ERROR("--dump can't be combined with other options");
>                          return false;
> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index 5b600bbf2389..d67b80251eec 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -131,6 +131,27 @@ static struct instruction *prev_insn_same_sym(struct objtool_file *file,
>          for (insn = next_insn_same_sec(file, insn); insn;               \
>               insn = next_insn_same_sec(file, insn))
> 
> +static struct instruction *find_insn_containing(struct objtool_file *file,
> +                                               struct section *sec,
> +                                               unsigned long offset)
> +{
> +       struct instruction *insn;
> +
> +       insn = find_insn(file, sec, 0);
> +       if (!insn)
> +               return NULL;
> +
> +       sec_for_each_insn_from(file, insn) {
> +               if (insn->offset > offset)
> +                       return NULL;
> +               if (insn->offset <= offset && (insn->offset + insn->len) > offset)
> +                       return insn;
> +       }
> +
> +       return NULL;
> +}
> +
> +
>   static inline struct symbol *insn_call_dest(struct instruction *insn)
>   {
>          if (insn->type == INSN_JUMP_DYNAMIC ||
> @@ -4529,6 +4550,61 @@ static int validate_reachable_instructions(struct objtool_file *file)
>          return 0;
>   }
> 
> +static int is_in_pvh_code(struct instruction *insn)
> +{
> +       struct symbol *sym = insn->sym;
> +
> +       return sym && !strcmp(sym->name, "pvh_start_xen");
> +}
> +
> +static int validate_pie(struct objtool_file *file)
> +{
> +       struct section *sec;
> +       struct reloc *reloc;
> +       struct instruction *insn;
> +       int warnings = 0;
> +
> +       for_each_sec(file, sec) {
> +               if (!sec->reloc)
> +                       continue;
> +               if (!(sec->sh.sh_flags & SHF_ALLOC))
> +                       continue;
> +
> +               list_for_each_entry(reloc, &sec->reloc->reloc_list, list) {
> +                       switch (reloc->type) {
> +                       case R_X86_64_NONE:
> +                       case R_X86_64_PC32:
> +                       case R_X86_64_PLT32:
> +                       case R_X86_64_64:
> +                       case R_X86_64_PC64:
> +                       case R_X86_64_GOTPCREL:
> +                               break;
> +                       case R_X86_64_32:
> +                       case R_X86_64_32S:

That looks very specific to X86, should it go at another place ?

If it can work for any architecture, can you add generic macros, just 
like commit c1449735211d ("objtool: Use macros to define arch specific 
reloc types") then commit c984aef8c832 ("objtool/powerpc: Add --mcount 
specific implementation") ?

> +                               insn = find_insn_containing(file, sec, reloc->offset);
> +                               if (!insn) {
> +                                       WARN("can't find relocate insn near %s+0x%lx",
> +                                            sec->name, reloc->offset);
> +                               } else {
> +                                       if (is_in_pvh_code(insn))
> +                                               break;
> +                                       WARN("insn at %s+0x%lx is not compatible with PIE",
> +                                            sec->name, insn->offset);
> +                               }
> +                               warnings++;
> +                               break;
> +                       default:
> +                               WARN("unexpected relocation type %d at %s+0x%lx",
> +                                    reloc->type, sec->name, reloc->offset);
> +                               warnings++;
> +                               break;
> +                       }
> +               }
> +       }
> +
> +       return warnings;
> +}
> +
>   int check(struct objtool_file *file)
>   {
>          int ret, warnings = 0;
> @@ -4673,6 +4749,12 @@ int check(struct objtool_file *file)
>                  warnings += ret;
>          }
> 
> +       if (opts.pie) {
> +               ret = validate_pie(file);
> +               if (ret < 0)
> +                       return ret;
> +               warnings += ret;
> +       }
> 
>          if (opts.stats) {
>                  printf("nr_insns_visited: %ld\n", nr_insns_visited);
> diff --git a/tools/objtool/include/objtool/builtin.h b/tools/objtool/include/objtool/builtin.h
> index 2a108e648b7a..1151211a5cea 100644
> --- a/tools/objtool/include/objtool/builtin.h
> +++ b/tools/objtool/include/objtool/builtin.h
> @@ -26,6 +26,7 @@ struct opts {
>          bool uaccess;
>          int prefix;
>          bool cfi;
> +       bool pie;
> 
>          /* options: */
>          bool backtrace;
> --
> 2.31.1
>